Initiator/hydroxide and initiator/alkoxide complexes, systems comprising the complexes, and polymerized compositions made therewith

ABSTRACT

Initiator systems of the invention comprise: a complexed initiator comprising at least one of a complex of a complexing agent comprising at least one hydroxide and an initiator or a complex of a complexing agent comprising at least one alkoxide and an initiator; and a decomplexer. The initiator systems are useful for initiating polymerization of at least one monomer to form polymerized compositions. Kits of the invention useful for forming the polymerized compositions comprise a polymerizable composition and an initiator component, wherein the initiator component comprises a complexed initiator of the invention. Bonding compositions can be prepared by mixing the polymerizable composition of the kit with the respective initiator component.

FIELD OF THE INVENTION

The present invention relates generally to complexes of initiators andcomplexing agents comprising at least one hydroxide, alkoxide, ormixtures thereof The complexes are useful in initiator systems forpolymerization of monomers.

BACKGROUND OF THE INVENTION

Systems for initiating the polymerization of monomers to makecompositions, such as adhesives, are known in the art. U.S. Pat. Nos.5,106,928, 5,286,821, and 5,310,835 to Skoultchi et al., for example,describe two-part initiator systems for initiating the polymerization ofacrylic monomers. The first part of these two-part systems typicallyincludes a stable organoborane amine complex and the second partincludes an activator. The activator liberates the organoborane compoundby removing the amine group, thereby allowing the organoborane compoundto initiate the polymerization process. Activators are also sometimesreferred to as liberators or decomplexers.

Common complexes in such systems include complexes of an organoboraneand an amine. While such complexes may be useful in many applications,certain problems may arise due to the use of amine complexing agents insuch conventional complexes. For example, when the complexes contain aprimary amine, adhesives prepared therefrom may be prone todiscoloration, such as yellowing. Furthermore, when including reactivediluents, such as aziridine-functional materials described in PCTPublication No. WO 98/17,694, for example, in compositions containingthe complexes, the diluents may prematurely react with protic amines(i.e., those amines in which a nitrogen atom is bonded to at least onehydrogen atom) in such complexes, prematurely decomplexing theorganoborane initiator. This phenomenon may even be to such an extent asto prematurely initiate polymerization of monomers present with thecomplexes or to degrade efficacy of the initiators for polymerization ofsubsequently added monomers.

In light of these potential problems and the desire to providealternative formulations, further complexes are desirable, particularlyfor use in initiator systems, such as those used for polymerization ofadhesives useful for bonding low surface energy substrates.

Initiator systems of the invention comprise: a complexed initiatorcomprising at least one of a complex of a complexing agent comprising atleast one hydroxide and an initiator and a complex of a complexing agentcomprising at least one alkoxide and an initiator; and a decomplexer.Preferably, the initiator comprises an organoborane initiator.

Complexes of organoborane initiators and complexing agents of theinvention may be represented by the following general Formula (I):

wherein R¹ is an alkyl group having 1 to about 10 carbon atoms. R² andR³ may be the same or different and are selected from (i.e., they areindependently selected from) alkyl groups having 1 to about 10 carbonatoms and phenyl-containing groups. “Cx” represents a complexing agentof the invention. The value of “v” is selected so as to provide aneffective ratio of oxygen atoms of the alkoxides and/or hydroxides toboron atoms in the complex.

The initiator systems are useful for initiating polymerization of atleast one monomer. To initiate polymerization in such a manner, at leastone monomer is provided and then blended with the initiator system.Polymerization of the at least one monomer can be initiated as such.

In one embodiment, the complexed initiator comprises a complexing agentrepresented by Formula (II):

 (⁽⁻⁾O—R⁴)_(n)M^((m+))  (II)

wherein each R⁴ is independently selected from hydrogen or an organicgroup (e.g., an alkyl or alkylene group); M^((m+)) represents acountercation (comprising a monovalent cation, such as a Group IA metal(e.g., sodium and potassium) cation or onium, or a multivalent cation,such as a Group IIA metal (e.g., calcium and magnesium) cation); n is aninteger greater than zero; and m is an integer greater than zero.Preferably, n and m are equal. Preferably, each R⁴ is the same in acomplexing agent. Particularly preferred complexing agents comprisethose having a countercation comprising a cation selected from sodium,potassium, and tetraalkylammoniums.

According to another aspect of the invention, complexing agents of theinvention are used as part of a kit. In one embodiment, kits of theinvention comprise a polymerizable composition, wherein thepolymerizable composition comprises:

at least one polymerizable monomer, and

at least one decomplexer; and

an initiator component, wherein the initiator component comprises:

a complexed initiator comprising at least one of:

a complex of a complexing agent comprising at least one hydroxide and aninitiator, and

a complex of a complexing agent comprising at least one alkoxide and aninitiator, and

an optional diluent.

A bonding composition can be prepared by mixing the polymerizablecomposition of the kit with the respective initiator component. Thebonding composition can be used, for example, to prepare substrates atleast partially coated with the bonding composition and bonded articlescomprising a first substrate and a second substrate, with thepolymerized bonding composition adhesively bonding the first and secondsubstrates together. The bonding compositions are particularly usefulfor coating low surface energy substrates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention provides initiator systems capable of initiatingpolymerization. More specifically, the invention provides “initiatorsystems” comprising (1) a complexed initiator (for example, anorganoborane hydroxide, an organoborane alkoxide complex, or mixtures orcombinations thereof) and (2) a decomplexer.

In one aspect of the invention, the initiator system is part of amulti-part kit. Such kits comprise at least a first part (i.e., apolymerizable composition) and a second part (i.e., an initiatorcomponent) for initiating polymerization of the polymerizablecomposition. Most preferably, for ease of use, the kits comprise onlytwo parts. The two parts of the kit may be readily combined in aconvenient, commercially useful, whole number mix ratio of 1:10 or less,more preferably 1:4, 1:3, 1:2 or 1:1, such that they can be easily usedwith multi-part dispensers. Such dispensers are shown in U.S. Pat. Nos.4,538,920 and 5,082,147 and are available from ConProTec, Inc. (Salem,N.H.) under the trade designation, MIXPAC. The parts of the kit can bereadily mixed to form bonding compositions, which readily polymerize topolymers, for example, adhesives.

The “polymerizable composition” typically comprises at least onedecomplexer and at least one polymerizable monomer.

The “initiator component” typically comprises at least one complexedinitiator (e.g., an organoborane hydroxide complex, an organoboranealkoxide complex, or mixtures or combinations thereof) and an optionaldiluent. When mixed with the polymerizable composition, the decomplexerin the polymerizable composition liberates the initiator (e.g.,organoborane) from the complexing agent (e.g., a complexing agentcomprising at least one hydroxide, alkoxide, or mixtures thereof),enabling polymerization of the monomer(s) to be initiated. “Bondingcompositions” are those compositions resulting from mixing of thepolymerizable composition and the initiator component according to oneaspect of the invention. The bonding compositions are useful for bondinga wide variety of substrates, including substrates derived frompolymers, wood, ceramics, concrete, and metals. The bonding compositionsare especially useful for bonding low-surface energy substrates.

“Low surface energy substrates” are those that have a surface energy ofless than 45 mJ/m², more typically less than 40 mJ/m² or less than 35mJ/m². Included among such materials are, for example, polyethylene andpolypropylene.

Other polymers of higher surface energy that may also be usefully bondedwith the compositions of the invention include polycarbonate andpolymethylmethacrylate. However, the invention is not so limited; thecompositions may be used to bond any suitable substrate, such as thosederived from thermoplastics, as well as wood, ceramics, concrete, primedmetals, and the like.

“Polymerized compositions” (also referred to as polymers) are thosecompositions where substantially all of the monomers in the bondingcomposition are polymerized except for a typically unpolymerized amountas recognizable to one of ordinary skill in the art. Polymerizedcompositions according to the invention may be used in a wide variety ofways, including, for example, as adhesives, bonding materials, sealants,coatings, and injection molding resins. The polymerized compositions mayalso be used as matrix resins in conjunction with glass, carbon, andmetal fiber mats, such as those used in resin transfer moldingoperations. The polymerized compositions may further be used asencapsulants and potting compounds, such as in the manufacture ofelectrical components, printed circuit boards, and the like. Those ofordinary skill in the art will recognize a wide variety of otherapplications in which the polymerized compositions are useful.

Initiator Component

Complexed Initiator

In general, complexed initiators of the invention are complexes of aninitiator and a complexing agent, specifically complexing agentcomprising at least one hydroxide, alkoxide, or mixtures thereof A“complex” is readily understood by one of ordinary skill in the art tobe a tightly coordinated salt formed by association of a Lewis acid(e.g., initiator) and a Lewis base (e.g., hydroxide or alkoxide).

Any suitable complexing agent comprising at least one hydroxide,alkoxide, or mixtures or combinations thereof, may be used for thecomplexing agent, as long as the complexing agent is reactive with thedecomplexer (if any) with which it is to be used. Furthermore, thecomplexing agent should also be capable of forming a complex with theinitiator with which it is used.

Any suitable initiator, or combination thereof, may be used in theinvention, as long as the initiator is capable of forming a complex withthe complexing agent. Furthermore, the initiator should also be capableof initiating polymerization of monomers with which it is to be used.

According to one aspect of the invention, the initiator is as anorganoborane. Complexes of organoborane initiators and complexing agentsof the invention may be represented by the following general Formula(I):

wherein R¹ is an alkyl group having 1 to about 10 carbon atoms. R² andR³ may be the same or different and are selected from (i.e., they areindependently selected from) alkyl groups having 1 to about 10 carbonatoms and phenyl-containing groups. Preferably, R¹, R² and R³ areindependently selected from alkyl groups having 1 to about 5 carbonatoms. Accordingly, R¹ R² and R³ may all be different, or more than oneof R¹, R² and R³ may be the same. Most preferably, R¹, R² and R³ are thesame.

Together, R¹, R² and R³, along with the boron atom (B) to which they areattached, form the initiator. Specific organoborane initiators include,for example, trimethylborane, triethylborane, tri-n-propylborane,triisopropylborane, tri-n-butylborane, triisobutylborane, andtri-sec-butylborane.

“Cx” in Formula I represents a complexing agent of the invention, whichis described further below.

The value of “v” is selected so as to provide an effective ratio ofoxygen atoms of the alkoxides and/or hydroxides to boron atoms in thecomplex. The ratio of oxygen atoms of the alkoxides and/or hydroxides toboron atoms in the complex should broadly be about 0.5:1 to about 4:1,preferably about 1:1 to about 2:1, more preferably about 1:1 to about1.5:1, and most preferably about 1:1.

Complexing Agent

The following terms will hereinafter be used to more particularlydescribe the complexing agent of the invention:

The terms “monovalent organic group” and “multivalent organic group”mean an organic moiety wherein the available valencies are on carbonatoms. Monovalent organic groups have one available valency.Accordingly, multivalent organic groups have more than one availablevalency.

The “organic groups” can be aliphatic groups or cyclic groups. In thecontext of the present invention, the term “aliphatic group” means asaturated or unsaturated, linear or branched, hydrocarbon group. Thisterm is used to encompass alkylene, alkenylene, alkynylene, alkyl,alkenyl, and alkynyl groups, for example. The term “alkyl group” means amonovalent, saturated, linear or branched, hydrocarbon group (e.g., amethyl, ethyl, isopropyl, t-butyl, heptyl, dodecyl, octadecyl, amyl, or2-ethylhexyl group, and the like). The term “alkylene” means amultivalent, saturated, linear or branched hydrocarbon group. The term“alkenyl group” means a monovalent, unsaturated, linear or branched,hydrocarbon group with one or more carbon-carbon double bonds (e.g., avinyl group). The term “alkenylene” means a multivalent, unsaturated,linear or branched, hydrocarbon group with one or more carbon-carbondouble bonds. The term “alkynyl group” means a monovalent, unsaturated,linear or branched, hydrocarbon group with one or more carbon-carbontriple bonds. The term “alkynylene” means a multivalent, linear orbranched, hydrocarbon group with one or more carbon-carbon triple bonds.

The term “cyclic group” or “cyclic structure” means a closed ringhydrocarbon group that is classified as an alicyclic group, aromaticgroup, or heterocyclic group. The term “alicyclic group” means a cyclichydrocarbon group having properties resembling those of aliphaticgroups. The term “aromatic group” or “aryl group” means a mononucleararomatic hydrocarbon group or polynuclear aromatic hydrocarbon group.

Organic groups or organic linking groups, as used herein, can includeinternal (i.e., not terminal) heteroatoms (e.g., O, N, or S atoms), suchas in the case of heterocyclic groups, as well as internal functionalgroups (e.g., carbonyl groups).

Cx in Formula (I) represents a complexing agent comprising at least onehydroxide, alkoxide, or mixtures thereof. Preferably, Cx and complexingagents of the invention are represented by the following Formula (II):

(⁽⁻⁾O—R⁴)_(n) ^(M) ^((m+))  (II)

Each R⁴ is independently selected from hydrogen or an organic group andeach of n and m are integers greater than zero.

Each R⁴ may be hydrogen in a complexing agent or each R⁴ may be anorganic group in a complexing agent. When any R⁴ is hydrogen, thecomplexing agent is said to comprise at least one hydroxide. When any R⁴is an organic group, the complexing agent is said to comprise at leastone alkoxide. Preferred alkoxides are those where R⁴ is an alkyl groupor an alkylene group. The complexing agent may also include a mixture ofat least one hydroxide and at least one alkoxide.

Typically, n is 1 or 2 and m is 1 or 2. Preferably, n and m are the sameinteger, most preferably 1.

In general, the complexing agent is used in the form of a salt. That is,the complexing agent is stabilized by a suitable countercation such thatthe complexing agent is capable of complexing the initiator. Thus, inFormula II, M^((m+)) represents a countercation that stabilizes thecomplexing agent.

Any suitable cation or combinations thereof can be used forcountercations of the invention. The cations can be monovalent ormultivalent, as indicated by the superscript, “m+.” When “m+” is 1, thecation is monovalent. For example, monovalent cations of the Group IAmetals (e.g., lithium, sodium, and potassium) can be used. Othersuitable monovalent cations include oniums, which generally conform tothe following Formula (III):

 (R⁵)_(z)(X⁽⁺⁾)  (III)

Each R⁵ is independently selected from monovalent organic groups.Accordingly, each R⁵ in Formula m may be different, or more than one R⁵may be the same. In Formula III, z represents an integer greater thanone. Typically z is 2, 3, or 4. Typically, X is a Group VA, VIA, or VIIAmetalloid (e.g., nitrogen, sulfur, iodine, and phosphorus). Exemplaryonium cations include tetraalkylammoniums (e.g., tetramethylammonium andtetrabutylammounium), triphenylsulfonium, diphenyliodonium, andtetrabutylphosphonium.

When “m+” is greater than 1, the cation is multivalent. Exemplarymultivalent cations include those cations of the Group IIA metals (e.g.,calcium and magnesium).

Monovalent cations are preferred. Especially preferred are sodium,potassium, and tetraalkylammoniums.

Certain complexes comprising hydroxides are known in the art. Forexample, see certain of the chemical structures disclosed in Brown,Herbert C., Hydroboranes, pp. 55-56 (1962). However, the use of suchcomplexes in initiator systems of the invention has not been reported.

Hydroxides and alkoxides provide strong coupling to organoboranes, withthe resulting complexes having excellent oxidative stability. Thus, theuse of complexing agents comprising at least one hydroxide, alkoxide, ormixtures thereof is particularly beneficial, particularly in initiatorsystems of the invention.

Advantageously, preferred complexes of the invention are air stable. By“air stable” it is meant that, when the complexes are stored in a cappedvessel at room temperature (about 20° to about 22° C.) and underotherwise ambient conditions (i.e., not under a vacuum and not in aninert atmosphere), the complexes remain useful as polymerizationinitiators for at least about two weeks. Preferably, the complexes maybe readily stored under these conditions for many months and up to ayear or more.

Air stability of the complex is enhanced when the complex is acrystalline material (i.e., the complex is a solid at room temperature,but has a measurable melting point when measured according toDifferential Scanning Calorimetry). However, complexes of the inventionare air stable for at least six months even when they are liquids atroom temperature. In some embodiments, liquid complexes (i.e., thosecomplexes having a measurable melting point that is lower than roomtemperature when measured according to Differential ScanningCalorimetry) and solutions of liquid or solid complexes may be preferredbecause liquids are generally easier to handle and mix at roomtemperature than are solids. One of ordinary skill in the art is capableof readily determining whether a complex based on selected initiatorsand complexing agents is a liquid or solid at room temperature.

Particularly preferred “air stable” complexes are non-pyrophoric. Thatis, the complexes do not spontaneously combust or self-ignite. One ofordinary skill in the art is capable of readily determining whether acomplex based on selected initiators and complexing agents isnon-pyrophoric. For example, the Pyrophoricity Test described in theExamples, infra, is one method of determining whether a complex ispyrophoric.

Exemplary complexing agents useful in the preparation of complexes ofthe invention include those prepared from the following: sodiumhydroxide, tetrabutylammonium hydroxide, sodium methoxide, andtetrabutylammonium methoxide. Exemplary organoboranes useful in thepreparation of complexes of the invention include: triethylborane andtributylborane. It should also be noted that blends of differentcomplexes may be used in initiator systems of the invention.

Complexes of the invention may be readily prepared using knowntechniques. Typically, the complexing agent is combined with theinitiator in an inert atmosphere with slow stirring. An exotherm isoften observed and cooling of the mixture is therefore recommended. Ifthe ingredients have a high vapor pressure, it is desirable to keep thereaction temperature below about 70° C. to 80° C. Once the materialshave been well mixed, the complex is permitted to cool to roomtemperature (i.e., about 22° C. to about 25° C.). No special storageconditions are required although it is preferred that the complex bekept in a capped vessel in a cool, dark location. Advantageously, thecomplexes can be prepared in the absence of organic solvents that wouldlater have to be removed, although they could be prepared in solvent ifso desired.

The resulting complex is employed in an effective amount, which is anamount large enough to permit polymerization to readily occur to obtaina polymer (preferably, an acrylic polymer). According to one aspect ofthe invention, when the initiator comprises an organoborane, aneffective amount of the organoborane complex is an amount that providesabout 0.01 weight % boron to about 1.5 weight % boron, more preferablyabout 0.01 weight % boron to about 0.60 weight % boron, most preferablyabout 0.02 weight % boron to about 0.50 weight % boron, based on thetotal weight of the bonding composition, less the weight of fillers,non-reactive diluents, and other non-reactive components. If the amountof organoborane complex is too low, resulting polymerization may beincomplete or, in the case of adhesives, the resulting composition mayhave poor adhesion.

On the other hand, if the amount of organoborane complex is too high,then polymerization may proceed too rapidly to allow for effectivemixing and use of the resulting composition. Large amounts of thecomplex could also lead to the generation of large volumes of borane,which in the case of an adhesive, may weaken the bondline when used forbonding substrate(s). The useful rate of polymerization will depend inpart on the method of applying the composition to a substrate. Thus, afaster rate of polymerization may be accommodated by using a high-speed,automated industrial adhesive applicator rather than by applying thecomposition with a hand applicator or by manually mixing thecomposition.

Diluent

The initiator component may also contain any suitable diluent, orcombination thereof The diluent may be reactive or nonreactive withmonomers used in the polymerizable composition.

Preferably, the diluent is inert toward the complexing agent. That is,preferably the diluent is essentially free of moieties that are reactivewith the complexing agent (i.e., moieties that are susceptible to beingesterified by or hydrolyzed by the complexing agent) such that thecomplexing agent is incapable of complexing the initiator or such thatthe diluent is chemically modified in such a way that desired propertiesof the composition are affected.

Nonreactive diluents include plasticizers well known to those ofordinary skill in the art. Reactive diluents include, for example,aziridine-functional materials and maleate-functional materials. Forexample, such reactive diluents are described in PCT Publication No. WO98/17,694 and U.S. application Ser. No. 09/272,152, entitled“Organoborane Amine Complex Initiator Systems and PolymerizableCompositions Made Therewith, assigned to the assignee of the presentinvention.

An “aziridine-functional material” refers to an organic compound havingat least one aziridine ring or group,

the carbon atom(s) of which may optionally be substituted by short chaingroups (e.g., groups having 1 to about 10 carbon atoms, preferablymethyl, ethyl or propyl), so as to form, for example, methyl, ethyl orpropyl aziridine moieties.

Examples of useful, commercially available polyaziridines include thoseavailable under the following trade designations: CROSSLINKER CX-100(from Zeneca Resins; Wilmington, Mass.), XAMA-2 (from EIT, Inc.; LakeWylie, S.C.); XAMA-7 (from EIT, Inc.; Lake Wylie, S.C.), and MAPO (tris[1-(2-methyl) aziridinyl] phosphine oxide (from Aceto ChemicalCorporation; Flushing, N.Y.).

Quite advantageously, when used, the complex is carried by (e.g.,dissolved in or diluted by) the diluent or a blend of two or moredifferent diluents in the initiator component. Generally, the diluentshould not be reactive toward the complex and functions as an extenderfor the complex. Also advantageously, the diluent may generally increasethe spontaneous combustion temperature of the initiator component,increasing the non-pyrophoric characteristics of the initiatorcomponent.

The diluent should be generally soluble in monomers included in thepolymerizable composition, such that the parts of the kit can be readilymixed. By “soluble” is meant that no evidence of gross phase separationat room temperature (i.e., about 22° C. to about 25° C.) is visible tothe unaided eye. Similarly, the complex should also be soluble in thediluent, although slightly warming a mixture of the complex and thediluent may be helpful in forming a solution of the two at roomtemperature (i.e., about 22° C. to about 25° C.). Accordingly,preferably, if used, the diluent is a liquid at or near room temperature(i.e., within about 10° C. of room temperature) or forms a liquidsolution with the complex at or near room temperature.

The diluent is used in an effective amount. Generally, this is an amountof not more than about 50 weight %, preferably not more than about 25weight %, more preferably not more than about 10 weight %, based on thetotal weight of the bonding composition. However, substantial amounts(e.g., more than about 15 weight %, sometimes more than about 40 weight%) of the complex may be dissolved in the diluent, which facilitates theprovision of multi-part kits that can be combined in a commerciallyuseful mix ratio.

Polymerizable Composition

Decomplexer

The term “decomplexer” means a compound capable of liberating theinitiator (e.g., organoborane) from its complexing agent, therebyenabling initiation of the polymerization process. Decomplexers are alsosometimes referred to as “activators” or “liberators.” As used herein,each of these terms has the same meaning.

Any suitable decomplexer, or combinations thereof, can be used, such asisocyanates, acids, acid chlorides, sulfonyl chlorides, anhydrides,compounds capable of liberating any of the foregoing when combined withthe initiator component, and mixtures thereof. Examples of suitableacids include Lewis acids and Brönsted acids. Particularly suitabledecomplexers include lower molecular weight carboxylic acid decomplexersdescribed by Skoultchi et al. (U.S. Pat. Nos. 5,310,835 and 5,106,928),sulfonyl chlorides and acid chlorides of Fujisawa, Imai, and Mashuhara(Reports of the Institute for Medical and Dental Engineering, vol. 3, p.64 (1969)), bireactive decomplexers comprising isocyanate groupsdescribed by Deviny (PCT Publication No. WO97/07,171), anhydridedecomplexers described by Deviny (PCT Publication No. WO97/17,383),carboxylic acid decomplexers described by Deviny et al. (PCT ApplicationNo. US98/12,296, filed Jun. 12, 1998 and entitled “Initiator Systems andAdhesive Compositions Made Therewith”), and mixtures thereof All ofthese publications are incorporated herein by reference.

The decomplexer is employed in an effective amount (i.e., an amounteffective to promote polymerization by liberating the initiator from itscomplexing agent, but without materially adversely affecting desiredproperties of the ultimate polymerized composition). As recognizable toone of ordinary skill in the art, too much of the decomplexer may causepolymerization to proceed too quickly and, in the case of adhesives, theresulting materials may demonstrate inadequate adhesion to low energysurfaces. However, if too little decomplexer is used, the rate ofpolymerization may be too slow and the resulting polymers may not be ofadequate molecular weight for certain applications. A reduced amount ofdecomplexer may be helpful in slowing the rate of polymerization if itis otherwise too fast. Thus, within these parameters, the decomplexer istypically provided in an amount such that the ratio of hydroxide- oralkoxide-reactive groups in the decomplexer(s) (e.g., acid groups oranhydride groups) to hydroxide and alkoxide groups in the complexingagent(s) is in the range of 0.5:1.0 to 3.0:1.0. For better performance,preferably the ratio of hydroxide- or alkoxide-reactive groups in thedecomplexer(s) to hydroxide and alkoxide groups in the complexingagent(s) is in the range of 0.5:1.0 to 1.0:1.0, preferably about1.0:1.0.

Monomers

The initiator system of the invention can be used to initiate thepolymerization of any suitable monomer(s). Broadly, the polymerizablecomposition includes at least one ethylenically unsaturated monomercapable of free radical polymerization. Numerous compounds containingethylenic unsaturation can be used in the polymerizable composition.Preferably, the composition includes at least one (meth)acrylic monomer,most preferably a methacrylic monomer. Particularly preferred are(meth)acrylic acid derivatives, such as those including esters and/oracid amides. Suitable are, for example, the (meth)acrylic esters ofmonohydric alcohols, particularly alkanols having from 1 to 12 carbonatoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl(meth)acrylate, and ethylhexyl (meth)acrylate; the (meth)acrylic acidesters of polyhydric alcohols, such as ethylene glycol, diethyleneglycol, polyethylene glycol, and trimethylol propane; the di- andmono(meth)acrylic acid esters of glycerin; the di(meth)acrylic acidesters of triethylene glycol and tetraethylene glycol; thedi(meth)acrylic acid esters of dipropylene glycol, tripropylene glycol,tetrapropylene glycol and pentapropylene glycol; and the di(meth)acrylicesters of ethoxylated or propoxylated diphenylolpropane.

Basically suitable are also polymerizable monomers, such as vinylacetate; vinyl halides, such as vinyl chloride, vinyl fluoride, vinylbromide; styrene; and divinyl-benzene. These compounds, however, aregenerally used only in subordinate amounts in the polymerizablecompositions.

Further suitable are acid amides, such as: acrylamide; N-methylacrylamide; N-methyl methacrylamide; N,N-dimethyl acrylamide;N,N-dimethyl methacrylamide; N-ethyl methacrylamide; N,N-diethylacrylamide; N,N-diethyl methacrylamide; N-isopropyl acrylamide; N-butylacrylamide; N-butyl methacrylamide; N-t-butyl acrylamide; N,N-dibutylmethacrylamide; N-phenyl acrylamide; N-(acryloyl)morpholine;N-(acryloyl)piperidine; N-(methacryloyl)piperidine;N-(1,1-dimethyl-3-oxobutyl)-acrylamide; N-1,3,3-tetramethylbutylacrylamide; dimethylene-bis-(meth)acrylamide;tetramethylene-bis-(meth)acrylamide;trimethylhexamethylene-bis-(meth)acrylamide;tri(meth)acryloyldiethylenetriamine; and similar compounds.

In general, the emphasis is on monomers with one or two olefinic doublebonds in the molecule, preferably one olefinic double bond. Theadditional use of higher unsaturated components is not excluded, but itmust be kept in mind that their presence can lead to embrittling of thepolymerized compositions.

Additives

Bonding compositions of the present invention may also comprise furtheroptional additives. Generally, such additives are present in thepolymerizable composition of the kit. Thus, the polymerizablecomposition may further comprise a variety of optional additives.

One particularly useful additive is a thickener, such as medium (about40,000) molecular weight polybutyl methacrylate that may generally beincorporated in an amount of up to about 50 weight %, based on the totalweight of the polymerizable composition. Thickeners may be employed toincrease the viscosity of the resulting bonding composition to a moreeasily applied viscous syrup-like consistency.

Another particularly useful additive is an elastomeric material. Thesematerials can improve the fracture toughness of bonding compositionsmade therewith, which can be beneficial when, for example, bondingstiff, high yield strength materials (e.g., metal substrates that do notmechanically absorb energy as easily as other materials, such asflexible polymeric substrates). Such additives can generally beincorporated in an amount of up to about 50% by weight, based on thetotal weight of the polymerizable composition.

Core-shell polymers can also be added to the polymerizable compositionto modify spreading and flow properties of the bonding composition.These enhanced properties may be manifested by a reduced tendency forthe bonding composition to leave an undesirable “string” upon dispensingfrom a syringe-type applicator, or sag or slump after having beenapplied to a vertical surface. Accordingly, use of more than about 20%by weight, based on total weight of the polymerizable composition, of acore-shell polymer additive may be desirable for achieving improvedsag-slump resistance. Core-shell polymers can also improve the fracturetoughness of bonding compositions made therewith, which can bebeneficial when, for example, bonding stiff, high yield strengthmaterials (e.g., metal substrates that do not mechanically absorb energyas easily as other materials, such as flexible polymeric substrates).

Small amounts of inhibitors, such as hydroquinone monomethyl ether maybe used in the polymerizable compositions, for example, to prevent orreduce degradation of the monomers during storage. Inhibitors may beadded in an amount that does not materially affect the rate ofpolymerization or the ultimate properties of polymers made therewith.Accordingly, inhibitors are generally useful in amounts of about100-10,000 ppm based on the total weight of the monomers in thepolymerizable composition.

Other possible additives include non-reactive colorants, fillers (e.g.,carbon black, hollow glass/ceramic beads, silica, titanium dioxide,solid glass/ceramic spheres, and chalk), and the like. The variousoptional additives are employed in any amount, but generally amountsthat do not significantly adversely affect the polymerization process orthe desired properties of polymers made therewith.

Bonding Compositions

The parts of the kits (i.e., the polymerizable composition and theinitiator component) are blended as would normally be done when workingwith such materials. The initiator component is added to thepolymerizable composition shortly before it is desired to use thebonding composition.

Once the parts of the kit have been combined to form a bondingcomposition, the composition should be used quickly, as the useful potlife may be short depending upon the monomers, the amount of theinitiator component, the temperature at which the bonding is to beperformed, the presence or absence of crosslinking agents, and whether adiluent is used. Preferably, to improve bonding, it is desirable to keepthe initial bonding temperature below about 40° C., preferably below 30°C., and most preferably below about 25° C. Accordingly, the bondingprocess can be carried out at room temperature (i.e., about 22° C. toabout 25° C.).

The bonding composition is applied to one or both substrates to bebonded and then the substrates are joined together with pressure toforce excess bonding composition out of the bond line. This also has theadvantage of displacing bonding composition that has been exposed to airand that may have begun to oxidize. In general, the bonds should be madeshortly after the bonding composition has been applied to thesubstrate(s), preferably within about 10 minutes. The typical bond linethickness is about 0.1 to 0.3 millimeters.

The bonds may cure (i.e., polymerize) to a reasonable green strength,i.e., to permit handling of such bonded articles within about 2-3 hours.Full bond strength will generally be reached in about 24 hours underambient conditions. However, post-curing with heat may be used, ifdesired.

In one preferred embodiment, the bonding compositions are coated on alow surface energy substrate. In another preferred embodiment, bondedarticles comprise a first substrate and a second substrate (preferablyat least one of which is a low surface energy polymeric material)adhesively bonded together by a layer of a bonding composition accordingto the invention.

The invention will be more fully appreciated with reference to thefollowing nonlimiting examples. These examples are merely forillustrative purposes only and are not meant to be limiting on the scopeof the appended claims. All parts, percentages, ratios, etc. in theexamples and the rest of the specification are by weight unlessindicated otherwise.

EXAMPLES

Various tradenames and abbreviations used in the examples are definedaccording to the following schedule:

Abbreviation/ Tradename Description BA Butyl acrylate, available fromAldrich Chemical Company; Milwaukee, WI BLENDEX 360 Trade designationfor a core-shell toughener available from GE Specialty Chemicals;Parkersburg, WV CAB-O-SIL TS 720 Trade designation for fumed silicaavailable from Cabot Corporation; Tuscola, IL CROSSLINKER Tradedesignation for trimethylolpropane tris(3-(2- CX-100 ormethylaziridino)propionate, commercially available CX-100 from ZenecaResins; Wilmington, MA ELVACITE 2010 Trade designation for poly(methylmethacrylate) available from ICI Acrylics; Wilmington, DE HDPEHigh-density polyethylene, available from Cadillac Plastic; Minneapolis,MN KOtBu Potassium tert-butoxide, available from Aldrich ChemicalCompany; Milwaukee, WI MAA Methacrylic acid, available from AldrichChemical Company; Milwaukee, WI MIXPAC SYSTEM Trade designation for a10:1 volume ratio dual 50 syringe applicator, Kit No. MP-050-10-09,commercially available from ConProTec; Salem, NH MMA Methylmethacrylate, available from Aldrich Chemical Company; Milwaukee, WINaOH Sodium hydroxide, available from Aldrich Chemical Company;Milwaukee, WI NaOMe Sodium methoxide, available from Aldrich Chemi- calCompany; Milwaukee, WI P25 Trade designation for titanium dioxideavailable from Degussa Corporation; Chester, PA poly(MMA-co-EA)poly(methyl methacrylate-co-ethyl acrylate), commercially availableunder catalog number 18224-9 from Aldrich Chemical Company; Milwaukee,WI. PP Polypropylene, available from Cadillac Plastic; Minneapolis, MNPTFE Polytetrafluoroethylene, available from Cadillac Plastic;Minneapolis, MN TEB Triethylborane, available from Aldrich ChemicalCompany; Milwaukee, WI THF Tetrahydrofuran, available from AldrichChemical Company; Milwaukee, WI

Overlap Shear Bond Strength Test

Each bonding composition was applied directly onto an untreated 2.5cm×10 cm×0.3 cm (1 inch×4 inch×0.125 inch) test panel (0.2 millimeter (8mil)-diameter glass bead spacers were added to the bonding composition)and a bare second test panel was immediately placed against the bondingcomposition on the first test panel so that the overlapped area was 1.3cm×2.5 cm (0.5 inch×1 inch). A clamp was applied to the overlapped area.The test panels were either polytetrafluoroethylene (PTFE), high-densitypolyethylene (HDPE) or polypropylene (PP), as noted in the particularexamples, all panels of which are commercially available from CadillacPlastic; Minneapolis, Minn. A small amount of bonding compositionsqueezed out of the overlapped area and was allowed to remain.

The bonds were allowed to cure for at least 48 hours at 22° C. Theclamps were then removed, and the overlap bonds were tested in shear(OLS) on a tensile tester at a crosshead speed of 1.27 cm/minute (0.5inch/minute). The overlap shear values were recorded in pounds andconverted into pounds per square inch (psi) and megapascals (MPa).

Preferably, for adequate bonding performance, the OLS values were atleast about 150 psi (1.03 MPa), more preferably at least about 300 psi(4.14 MPa) for the PTFE; at least about 500 psi (3.45 MPa), morepreferably at least about 700 psi (4.83 MPa) for the HDPE; and at leastabout 600 psi (4.14 MPa), more preferably at least about 800 psi (5.52MPa) for the PP. Also, for diverse utility, it is preferable that aparticular adhesive is able to adequately bond at least two differenttypes of low surface energy substrates. Accordingly, more preferably, aparticular adhesive is able to adequately bond all of PTFE, HDPE, andPP. Most preferably, a particular adhesive is able to adequately bondPTFE to an OLS value of at least about 300 psi (4.14 MPa), HDPE to anOLS value of at least about 700 psi (4.83 MPa), and PP to an OLS valueof at least about 800 psi (5.52 MPa).

Organoborane Complex Preparation Examples 1-3

Sodium hydroxide, sodium methoxide, and potassium tert-butoxidecomplexes with triethylborane were prepared by combining equimolarquantities of a complexing agent with triethylborane under a nitrogenatmosphere without external temperature control. The complexes wereprepared as aqueous, methanolic, and tetrahydrofuran solutions,respectively. Aqueous sodium hydroxide and triethylborane formedseparate phases initially, becoming homogeneous after several hours ofmixing at room temperature. The quantities of each component and type ofcomplexing agent are noted in Table 1.

TABLE 1 Weight Complexing Agent (grams (millimoles)) Weight ComplexingAgent [weight of solution - Triethylborane Ex. (weight % in solution)grams] (grams (millimoles)) 1 Sodium hydroxide 0.40 (10) 0.98 (10) (50%in water) [0.80] 2 Sodium methoxide 0.54 (10) 0.98 (10) (25% inmethanol) [2.16] 3 Potassium tert- 1.12 (10) 0.98 (10) butoxide [3.12](36% in THF)

Pyrophoricity Test

The pyrophoricity of each organoborane complex (Example 1-3) was testedby applying a 0.05 ml aliquot to a 1″×1″ paper towel fragment in air toproduce a treated paper towel. If the treated paper towel self-ignited(i.e., spontaneously combusted) within one minute or less, thecomposition is considered pyrophoric. If the treated paper towel did notself-ignite after ten minutes, the composition is considerednon-pyrophoric. Results of whether or not each composition is pyrophoricaccording to the above-described test are tabulated in Table 2.

TABLE 2 Ex. Complexing Agent Pyrophoric? 1 NaOH No 2 NaOMe No 3 KOtBu No

¹H-NMR Spectroscopy (Proton Nuclear Magnetic Resonance Spectroscopy)

¹H-NMR chemical shift in CDCl₃ of methylene groups adjacent to boron insodium methoxide triethylborane complexes further demonstrated thestrong coupling of organoborane complexes useful in the invention. ¹H-NMR shifts for methylene groups adjacent to boron in organoboranecomplexes useful in the invention appear below about 80.5. The ¹H-NMRshift for methylene groups adjacent to boron is about δ1.2 fortriethylborane itself The composition prepared in Example 2 was testedusing ¹H-NM spectroscopy, with the result indicated in Table 3.

TABLE 3 ¹H-NMR Shift Ex. Complexing Agent of B-CH₂ 2 sodium methoxide0.10

Bonding Composition Preparation Example 4

Initiator Component

The triethylborane complex of Example 1 (1.78 grams solution) (TEB-NaOH)was dissolved in 1.55 grams CROSSLINKER CX-100. Air bubbles in thecomposition were allowed to rise and escape.

Polymerizable Composition

A polymerizable composition was prepared by combining 39.00 grams methylmethacrylate (MMA), 28.00 grams butyl acrylate (BA), 5.35 gramsmethacrylic acid (MAA), and 30.00 grams poly(MMA-co-EA). Air bubbleswere removed from the composition using brief stirring under vacuum.

Bonding Composition

The polymerizable composition and initiator component were packaged in aMIXPAC SYSTEM 50 applicator, the larger cylinder of the applicatorholding the polymerizable composition and the smaller cylinder holdingthe initiator component. The two parts were combined by simultaneousextrusion through a 10 centimeter (4 inch) long, 17-stage static mixnozzle, Part No. MX 4-17-5, commercially available from ConProTec;Salem, N.H. Test specimens were prepared and tested according to theOverlap Shear Bond Strength Test, except that steel wire spacers (0.2millimeter (8 mil) diameter) were inserted into the wet adhesive betweenthe first and second untreated test panels before clamping. Results ofoverlap shear testing for Example 4 are tabulated in Table 4.

TABLE 4 Overlap Shear Test Panel MPa (psi) HDPE 4.22 (612) PP 4.03 (585)PTFE 1.71 (248)

Example 5

Initiator Component

An initiator component was prepared combining an aqueous triethylboranecomplex prepared as in Example 1 (6.57 grams solution) (TEB-NaOH), 11.05grams CX-100, 1.42 grams CAB-O-SIL TS 720, and 0.96 gram P25.

Polymerizable Composition

A polymerizable composition was prepared by heating a slurry containing19.85 grams methyl methacrylate (MMA), 9.75 grams butyl acrylate (BA),2.40 grams methacrylic acid (MAA), 13.50 grams BLENDEX 360, and 4.55grams ELVACITE 2010 for three hours at 70° C. The resultant dispersionwas allowed to cool and was then sheared aggressively with a saw-toothedblade of a laboratory dispersator, commercially available from PremierMill Corporation; Reading, Pa. Air bubbles were removed from thecomposition using brief stirring under vacuum.

The polymerizable composition and initiator component were packaged andevaluated as described in Example 4. Results from testing according tothe Overlap Shear Bond Strength Test are tabulated in Table 5.

TABLE 5 Overlap Shear Test Panel MPa (psi) HDPE 5.60 (812) PP 3.89 (564)PTFE 1.28 (185)

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of the invention. It should be understood that this inventionis not limited to the illustrative embodiments set forth herein.

What is claimed is:
 1. An organoborane initiator system for free radicalpolymerization comprising: a complexed organoborane initiator comprisingat least one of: a complex comprising a complexing agent comprising atleast one hydroxide salt and an organoborane initiator; and a complexcomprising a complexing agent comprising at least one alkoxide salt andan organoborane initiator; and a decomplexer.
 2. The initiator system ofclaim 1, wherein the complexing agent comprises at least one hydroxidesalt.
 3. The initiator system of claim 1, wherein the complexing agentcomprises at least one alkoxide salt.
 4. The initiator system of claim1, wherein the complexed initiator comprises a complexing agentrepresented by Formula (II): (⁽⁻⁾O—R⁴)_(n)M^((m+))  (II) wherein: eachR⁴ is independently hydrogen or an organic group; M^((m+)) represents acountercation; n is an integer greater than zero; and m is an integergreater than zero.
 5. The initiator system of claim 4, wherein M^((m+))comprises a monovalent cation.
 6. The initiator system of claim 5,wherein M^((m+)) comprises an onium cation.
 7. The initiator system ofclaim 4, wherein n and m are equal.
 8. The initiator system of claim 4,wherein each R⁴ is independently an alkyl or alkylene group.
 9. Theinitiator system of claim 4, wherein each R⁴ is hydrogen.
 10. Theinitiator system of claim 4, wherein M^((m+)) is selected from the groupconsisting of cations of sodium, potassium, tetraalkylammoniums, andcombinations thereof.